When a large volume of liquefied gas whose vapor pressure is low and therefore vaporization volume is low at an ordinary temperature is necessary, methods to increase vaporization surface area or to raise the gas temperature are used. And increasing a diameter of a container of the gas, parallel connection of containers having a standard volume or heating the container is effective to realize the methods. Therefore, a system has been developed to supply huge volume of the gas constantly by the parallel connection of the containers having a standard volume which is easily available, heating the gas container or combination of them.
FIG. 7 shows an example 1 of conventional controlling method of a liquefied gas supply system (Patent Document 1). The control method of liquefied gas supply system is, as shown in FIG. 7, observing a remained volume of the liquefied gas in each cylinder by a volume indicator installed in each cylinder. And when the remaining volume of the gas decreased below a predetermined value, the supply is shut off by closing a controlled closing valve. The gas in each cylinder can be consumed to the minimum volume even when a decreasing speed of the gas in each cylinder is different in the system. However, a heating means to heat the gas in the cylinder is not installed.
FIG. 8 shows an example 2 of conventional controlling method of a liquefied gas supply system (Patent Document 2). The supply system and method of liquefied gas comprises a plurality of liquefied gas cylinders 21 and a gas reservoir (buffer tank) 24 before a pressure controlling pot 23 connected by gas piping lines 22, 25. The vaporized gas at normal temperature is introduced into the buffer tank through the piping and temporarily storaged there. The buffer tank plays a role as a temporary storage tank and when a sudden change of the amount of the gas consumption occurred, the gas in the buffer tank is supplied from the pressure controlling pot through the piping and can follow the consumption of the gas. However, a heating means to heat the gas in the cylinder is not installed in this example 2. Furthermore, there is no description for a detection means of remaining volume of the liquefied gas in the cylinder.
FIG. 9 shows an example 3 of a conventional supply method of liquefied gas (Patent Document 3). As is shown in FIG. 9, the liquefied gas supplying method comprises liquefied gas cylinder 100, a first piping 105, a second piping 106 and a gas-flow detection means 104. And the liquefied gas cylinder 100, the first piping 105 and the second piping 106 are heated by a first heating means 101, a second heating means 102 and a third heating means 103, respectively which are controlled in response to a measured value obtained by the gas-flow detection means 104. Or the heating is controlled in response to the number of opened valve among a plurality of valves 131 to 140 provided after the second piping 106 instead of using the measured value obtained by the gas-flow detection means 104. This heating method has a condition that at least one valve among the valves should be opened and the gas is supplied constantly. However, the method disclosed in the Patent Document 3 uses only one liquefied gas cylinder 100 and not a plurality of cylinders. Nor any detection means of the remained volume in the liquefied gas cylinder is disclosed.
FIG. 10 shows an example 4 (related art) of a liquefied gas supply system using a plurality of gas containers. As is shown in FIG. 10, the system comprises a plurality of liquefied gas containers having a standard size and arranged in parallel, and each of the liquefied gas containers is heated separately and remained gas volume in each of the gas container is measured by a measurement device such as a weight scale. A heat controller system as heating means 3-1 to 3-n , heat measurement sensors 4-1 to 4-n , temperature controllers 5-1 to 5-n and heat output units 6-1 to 6-n and a measurement system of the liquefied gas volume in the containers as scales 2-1 to 2-n are installed and controlled separately.    [Patent Document 1]
JP Patent Kokai Publication No. JP-H11-226386A    [Patent Document 2]
JP Patent Kokai Publication No. JP-2003-28395A    [Patent Document 3]
JP Patent Kokai Publication No. JP-2006-161937A